(i) Field of the Invention
This invention relates to a pulse signal generator, for example, a pulse signal generator which generates different pulses according to the rotation direction of a disk-shaped rotator gear.
(ii) Description of the Related Art
In recent years, such a pulse signal generator using a magnetic device that can cause a large Barkhausen jump or Barkhausen effect as described in Japanese Patent No. 3,617,604 and other literatures has been developed. However, a traveling direction detector using this type of pulse signal generator, e.g. a detector for detecting the rotation direction of a rotator gear, has still not been available.
An example of the rotation direction detector is a detector which detects the positive rotation or negative rotation of a rotator gear by use of a semiconductor magnetic sensor (hall element or magnetoresistive element) having two detection sections, as disclosed in Japanese Patent Laid-Open Publication No. H9-32620. However, this device has problems that the output leading lines of the sensor are increased and that complicated rotation direction detecting means is required for control.
Further, Japanese Patent Laid-Open Publication No. H11-62687 discloses a device which uses two electromagnetic pickup sensors for a crank angle sensor and a cylinder detecting sensor in order to detect the rotation direction of an engine. However, since this device detects the rotation direction of the engine by comparing two signals from these crank angle sensor and cylinder detecting sensor with each other, the device has a problem that it can be used only for detection of the rotation direction of the engine.
In addition, Japanese Patent Laid-Open Publication No. 2002-213605 discloses a device which uses electromagnetic pickup sensors for detecting a vehicle speed and a traveling direction. This constitution requires two sensors and two rotors for detection.
Although the magnetic device that can cause a large Barkhausen jump (hereinafter may be simply referred to as “magnetic device”) is already well known as described in the above Japanese Patent No. 3,617,604, it will be briefly described hereinafter just to make sure. First, the structure and behavior of a generally known wire-shaped compound magnetic device will be described as an example. A thin wire obtained by drawing a ferromagnetic material has a unique magnetic properties in addition to its alloy composition. When twist stress is imposed on this ferromagnetic wire, the peripheral portion of the wire is twisted more severely and its central portion is twisted less severely, so that its peripheral portion and central portion have different magnetic properties. When the wire is so processed as to keep this state, a ferromagnetic wire whose peripheral portion and central portion have different magnetic properties is obtained. The magnetization direction of the peripheral portion is changed by a relatively small magnetic field. Meanwhile, the magnetization direction of the central portion is changed by a larger magnetic field. That is, a compound magnetic material having two different magnetic properties, i.e. a peripheral portion having a magnetic property which is relatively easily magnetized and a central portion which is less easily magnetized, in one magnetic wire is formed. This compound magnetic wire is uniaxially anisotropic. Hereinafter, the peripheral portion will be referred to as “soft layer”, the central portion will be referred to as “hard layer”, and such a compound magnetic wire will be referred to as “wire-shaped compound magnetic device”.
The hard layer and soft layer of this compound magnetic wire are initially not magnetized in a specific direction and are in a randomly magnetized state. When an external magnetic field which is strong enough to reverse the magnetization direction of the hard layer is applied parallel to the longitudinal direction or axial direction of this compound magnetic wire, the hard layer as well as the soft layer is magnetized in the same magnetization direction. Then, an external magnetic field capable of magnetizing only the soft layer is applied in the direction opposite to the previous direction. As a result, the compound magnetic wire is in a magnetized state in which the soft layer and the hard layer are magnetized in the opposite directions. Since the compound magnetic wire is uniaxially anisotropic, the magnetization direction of the soft layer is retained by the magnetization of the hard layer and the magnetized state is stable, even if the external magnetic field is removed in the above state. The above external magnetic field is referred to as “set magnetic field”. Then, an external magnetic field whose direction is opposite to the set magnetic field is applied to enhance the magnetic field. When the intensity of the external magnetic field exceeds certain critical intensity, the magnetization direction of the soft layer is revered immediately. This magnetic field is referred to as “critical magnetic field”. The above reverse phenomenon occurs such that the magnetic domain wall of the soft layer moves like an avalanche and a reaction occurs. As a result, the magnetization directions of the soft layer and hard layer becomes the same and the original state is reinstated. The applied external magnetic field is larger than the critical magnetic field. This magnetic field is referred to as “reset magnetic field (HR)”. The above phenomenon that the domain wall moves like an avalanche is referred to as “large Barkhausen jump”. The speed of the magnetic domain wall (change in magnetic flux density) is dependent only on this large Barkhausen jump and is not relevant to an external magnetic field.
Although the “magnetic device that can cause a large Barkhausen jump” has so far been described by use of the wire-shaped magnetic device as an example, it is not limited to such a wire-shaped compound magnetic device, and various other magnetic devices which show a similar behavior can also be used. Further, although the above compound magnetic device has the hard layer and the soft layer, the magnetic device that can cause a large Barkhausen jump may also be a magnetic device which does not have a compound layer of the hard layer and the soft layer. For example, it is possible to form a thin-film magnetic material by use of a thin-film formation technique as disclosed in Japanese Patent Laid-Open Publication No. H4-218950 and use the material as a thin-film magnetic device. Further, the magnetic device may be in the form of a thick film or a plate. Accordingly, the terms “magnetic device that can cause a large Barkhausen jump” as used herein include all of various magnetic devices that show the foregoing behavior.
Patent Literature 1
Japanese Patent No. 3,617,604
Patent Literature 2
Japanese Patent Laid-Open Publication No. H9-32620
Patent Literature 3
Japanese Patent Laid-Open Publication No. H11-62687
Patent Literature 4
Japanese Patent Laid-Open Publication No. 2002-213605
An object of the present invention is to provide a novel pulse signal generator which can be used to detect the traveling direction of an object to be detected by use of a magnetic device that can cause a large Barkhausen jump.